Buffered amino alcohol solutions of N-(n-butyl)thiophosphoric triamide (NBPT) and urea fertilizers using such solutions as urease inhibitors

ABSTRACT

Reduced volatility of urea fertilizers are prepared in accordance with the present invention by first preparing an N-(n-butyl)-thiophosphoric triamide (NBPT) solution by dissolving NBPT in a mixture of an amino alcohol having the formula 1—(H) x —N—((CH 2 ) m —OH) n  where m is 1-3, x is 0 or 1, and n is 2 when x is 1 and 3 when x is 0: or the formula 2—(H) y —N—((CH 2 )—CHOH—CH 3 ) z  such that the length of the carbon chain where the secondary hydroxyl group is located is 3, y is 0 or 1, and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acid having 6 or fewer carbon atoms. The solution is then combining with a urea fertilizer in granular or liquid form.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

Fertilizer materials derived primarily from urea with other additionaluseful additives and plant nutrient materials are treated with abuffered solution of N-(n-butyl) thiophosphoric triamide (NBPT)dissolved in a mixture of one or more amino alcohols with one or morecarboxylic acids having 6 or fewer carbon atoms to reduce nitrogenvolatilization. The solution may be applied as a coating for granularurea fertilizers, or mixed with an aqueous fertilizer solution.

(2) Description of the Prior Art

The degradation of urea to release ammonia when applied to the soil iswell known. The losses of applied nitrogen due to volatilization can besubstantial (see review by Terman “Volatilization Losses of Nitrogen asAmmonia from Surface Applied Fertilizers, Organic Amendments and CropResidues” in Advances in Agronomy 31: 189-223, 1979). The losses ofnitrogen from urea applied to the soil are dependent upon a number offactors including: soil pH, soil temperature, soil moisture, cationexchange capacity of the soil and soil organic matter content. Greaterlosses of nitrogen from urea are observed as the soil temperatureincreases, as the soil pH increases and as the organic matter contentincreases. Decreased nitrogen losses of nitrogen from urea are observedwhenever the soil moisture is high. In addition the depth of fertilizerplacement influences nitrogen losses and surface placements aregenerally subject to greater nitrogen loss. The relative humidity attime of fertilization can influence losses. Recent rainfall events willtend to reduce losses if sufficient water is present to distribute thefertilizer into the soil.

Methods for controlling volatile nitrogen loses from urea have includedthe application of metal salts of copper and zinc, boron compounds,organic urease inhibitors, acid coatings, polymer coatings, and reactionof urea with aldehydes to form a slow release molecular adduct (seebackground in Whitehurst. et. al. U.S. Pat. No. 6,830,603 which isincorporated by reference). A number of extended release products havebeen proposed to help control volatile nitrogen losses.

N-(n-butyl)-thiopsosphoric triamide (NBPT) is a known urease inhibitordescribed by (Kolc et. al. U.S. Pat. No. 4,530,714). The compound is awaxy solid with poor water solubility making it difficult to coat ureaand achieve adhesion of the compound. The compound undergoes hydrolysisand is thermally unstable.

The 714 patent describes the mixing of NBPT with organic solvents(acetone, disobutylketone, methanol, ethanol, 2-propanol,ether(diethyl), tolune, methylene chloride) to distribute the compoundinto the soil in an effective concentration range which can be anywherefrom 5 ppm to 100 ppm depending upon the soil. The organic solventsdescribed by the 714 patent are either too flammable for use or posesignificant health risks to be considered suitable for coating ureagranules.

In an alternate method, the 714 patent indicates that NBPT can be mixedwith solids such as gypsum or clay to distribute the compound into thesoil in an effective concentration.

Omilinsky et. al. (U.S. Pat. No. 5,698,003) describes the dissolution ofNBPT with a glycol such as propylene glycol or ethylene glycol andesters of glycols. Glycols are compounds with adjacent alcohol groups inthe chemical structure. The dissolution may contain a co-solvent liquidamide such as N-methyl-2-pyrrolidine and potentially a surfactant ordispersing agent such as polyethylene glycol or esters of polyethyleneglycol (polyether alcohols). The patent indicates that esters ofglycerol (a triol) may be used as the base solvent. Urea granulescontaining NBPT are prepared by mixing the urea granules with the NBPTdissolution solvent. Omilinsky et. al. teach that a drying agent such asclay or gypsum may be added to the compositions in the event that aproduct with excessive wetness is obtained.

Weston et. al (U.S. Pat. No. 5,352,265 and U.S. Pat. No. 5,364,438)teach the dissolution of NBPT in liquid amides such as 2-pyrrolidone orN-alkyl-2-pyrrolidones such as N-methyl-2-pyrrolidone to prepare bothsolid urea formulations (265 patent) or liquid formulations (438patent).

Hojjatie et. al. (US 2006/0185411) teach the use of a number of sulfursalts of calcium or magnesium (calcium polysulfide, thiosulfate,magnesium thiosulfate) as urease inhibitors to prepare granular orliquid urea compositions.

Quin (US 2004/0163434) teaches the formation of a sulfur coated ureawhich may contain the urease inhibitor NBPT supplied from a proprietaryliquid formulation sold as Agrotain® and distributed by AgrotainInternational LLC, Indiana, USA.

Sutton et. al. (U.S. Pat. No. 5,0247,689) teach the formation of aliquid fertilizer that includes urease inhibitors such as NBPT andnitrification inhibitors such as dicyandiamide in aqueous mixtures ofurea ammonium polyphosphate, ammonium thiosulfate and potentially otherplant growth improving compounds.

Sutton (US 2007/0295047) teaches the formation of a solid fertilizercomprised of urea and a urea-formaldehyde polymer which may additionallyinclude a urease inhibitor such as NBPT.

Sutton et. al. (US 2007/0157689) describes a fertilizer additivecomposed of urea, a urea-formaldehyde polymer and NBPT dissolved in anN-alkyl-2-pyrrolidone.

Urea is a high nitrogen analysis material which is often desirable as astarting material for making additional fertilizer products providingphosphorus or potassium as primary nutrients, calcium, magnesium orsulfur as secondary nutrients or micronutrients such as boron, copper,iron, manganese, molybdenum and zinc.

Whitehurst et. al. (603 patent) describe a coating methodology wherein aboron containing urease inhibitor composition may be used to addadditional nutrients such as phosphate, potassium, etc. The coating ofurea with other materials is known and the references in Whitehurst et.al. (603 patent) provides a partial summary of prior art in the area.The inhibitors and binders of this invention are aqueous mixtures thatinclude ethanolamine borates, diethanolamine borates or triethanolamineborates and mixtures of these.

Commercial products containing aqueous ethanolamine borates ortriethanolamine borates are distributed under the trade name ofARBORITE® by Encee Chemical Sales, North Carolina, USA. The product isfurther identified by a binder number for separation of the differentmixtures available.

SUMMARY OF THE INVENTION

Generally, reduced volatility urea fertilizers are prepared inaccordance with the present invention by first preparing anN-(n-butyl)-thiophosphoric triamide (NBPT) solution by dissolving NBPTin a mixture of an amino alcohol having the formula1—(H)_(x)—N—((CH₂)_(m)—OH)_(n) where m is 1-3, x is 0 or 1, and n is 2when x is I and 3 when x is 0: or the formula2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of the carbonchain where the secondary hydroxyl group is located is 3, y is 0 or 1,and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acid having 6or fewer carbon atoms. The solution is then combined with a ureafertilizer in granular or liquid form.

As used herein, the term “urea fertilizer” encompasses urea and mixturesof urea with other primary nutrients, secondary nutrients and/ormicronutrients. Preferably, urea comprises at least 40% by weight of theurea fertilizer. Unless otherwise noted all percentages refer to weightpercentages or parts per 100 parts. NBPT—N-(n-butylthiophosphorictriamide) is an item of commerce and is sold in various forms which maycontain impurities.

The amino alcohols required to practice the invention are thosecompounds which possess a primary, secondary or tertiary amine functionwith an alcohol functional group on an adjacent carbon to the nitrogenatom. The compounds will further have a pK_(a) of between about 7.5 and10. The following amino alcohols (alkanolamines) needed to practice theinvention are items of commerce:

MEA—ethanolamine

DEA—diethanolamine

TEA—triethanolamine

MIPA—monoisopropanolamine

DIPA—diisopropanolamine

The above materials are items of commerce and except for DIPA occur asliquids at room temperature. TEA and DEA may be obtained as mixtureswhich include MEA. DIPA may be obtained as mixture with MIPA.

The acids needed to practice the invention may be described ascarboxylic acids with 6 or fewer carbon atoms with or without hydroxylgroups. The acids required to practice the invention should have pKa'sof approximately 5 or less.

Acetic acid, propionic acid butyric, valeric and caproic acid are itemsof commerce. These acids may be obtained as a substantially purematerials or with small amount of water <10%. The acids may additionallyhave an alcohol group such as lactic acid (2-hydroxypropionic acid)which is an item of commerce. Other examples of hydroxyacids include thehydroxybutyric acids (2-hydroxy, 3-hydroxy, or 4 hydroxy-butanoicacids).

The term solubility limit as used below refers to the measurement ofmaximum amount of NBPT which will dissolve in a buffered mixtureprepared from the amino alcohols. To determine the solubility limit amixture is prepared by melting NBPT into a weighed amount of thebuffered liquid mixture of the invention at the desired concentration ofNBPT. The resulting mixture is observed over a period of time to assesswhether solids form upon standing. If solids form upon standing themixture is deemed unstable and the solubility limit is consideredexceeded.

All solubility limits are expressed in weight percentages and areunderstood to imply the limit of the solubility of NBPT.

Additionally, the practice of the invention may include other items ofcommerce including ethylene glycol and propylene glycol. The glycols canbe used as co-solvents or as agents to reduce viscosity of variousmixtures to control spreadability of a formulation.

The production of some coated products may include one or more sourcesof additional plant nutrients as water soluble salts such as potassiumchloride, potassium sulfate, and salts of iron, copper, zinc, manganese,and others; and partially water soluble salts such as gypsum, potassiummagnesium sulfate and others commonly employed in agricultural practice.The only requirement for the selection of the additional plant nutrientsource is that if be compatible with urea. Compatibility of manyfertilizer materials can be determined from the “Farm ChemicalsHandbook” published by Meister Publishing Co. Ohio, USA.

To make mixed fertilizer compositions using the invention, one or morematerials providing plant nutrients other than urea is preferably usedin a powdered form. The term powder for purposes of the invention shallmean any finely divided substance prepared by some dry grinding process.There are numerous forms of dry grinding equipment available includinghammer mills or pin mills, etc. A powder for purposes of the inventionshall imply any finely divided material with a particle size less than0.300 mm (300 μm).

Mixed fertilizer compositions are described by expressing the weightpercentage of the primary elements present in the following manner:XX-YY-ZZ; where XX is the percentage of nitrogen, YY is the phosphatepercentage expressed as P₂O₅, and ZZ is the potassium content expressedas the percentage K₂O. When secondary elements are present thepercentages are often listed after the primary elements in the ordercalcium, magnesium and sulfur or by stating the analysis for thesecondary element followed by the symbol for the element. For example a35-9-0-2Ca-2Mg,-3S would indicate a material (fertilizer) with 35%nitrogen, 9% P₂O₅, 0% K₂O, 2% Ca, 2% Mg and 3% S.

DETAILED DESCRIPTION OF THE INVENTION

To practice the invention, a buffered mixture is prepared from an aminoalcohol identified above by reaction of the amino alcohol with an acidselected from the short chain carboxylic acids which have pKa's of 5 orless. The reaction is carried out by mixing the amino alcohol with aquantity of acid such that the pH of the resulting mixture lies between8 and 10. The best performance is obtained whenever the pH of thebuffered mixture lies between 9 and 10.

The reaction of the amino alcohol with an acid forms the ammonium ionform of the amine and the neutralized acid becomes a carboxylate ion.Depending upon the pK_(a) of the amino alcohol, the mixture resultingfrom the reaction will contain the amino alcohol (alkanolamine), analkanolammoium ion, a carboxylate ion and water. The water is formed asa product of the neutralization reaction.

The reaction is exothermic and may require cooling. If the temperatureof the buffered mixture is above 60° C. it must be cooled beforeproceeding with the NBPT dissolution step.

Following preparation of the buffered mixture, NBPT is dissolved in thebuffered mixture to prepare urea containing compositions that includethis valuable urease inhibitor. The dissolution step for NBPT ispreferably carried out by the melting of the solid NBPT into thebuffered mixture. A temperature of 50° C. to 60° C. may be used to helpmelt NBPT into the buffered mixture in mixing equipment which avoidsexcessive aeration. The melting step may be accomplished using jacketedvessels or heating coils provided that the melt is swept away from theheat source by stirring the mixture as it forms using an agitator orcirculation pump to prevent a localized hot spot from forming. Themelting step is preferably performed using hot water to avoid thermaldamage to the NBPT. Steam may be used; however, both rapid circulationwhile mixing and temperature controls should be employed to reducethermal degradation of NBPT.

In the preferred embodiment of the invention; a buffered NBPT containingmixture is formed by mixing NBPT with a buffered mixture as definedabove sufficient to give a concentration from 2% NBPT to 40% NBPT byweight depending upon the solubility of limit of NBPT in the bufferedmixture.

To assist in the formulation processes described below, a dye orcolorant can be added to the buffered mixture containing mixture. Anycommonly used colorant including food dyes may be added to the mixtureto provide visual evidence of the uniformity of the distribution of thebuffered mixture containing NBPT as described below. Methylene blue is acommercially available blue colored substance which could be dissolvedin water or alcohol to add to the buffered NBPT containing mixture.

Once NBPT is dissolved the buffered mixture with or without a colorant,useful compositions can be obtained by contacting granular urea with theNBPT present. Coated granular urea containing products with from 0.050%to 0.25% NBPT can be made which have applications in agriculture orforestry where nitrogen fertilization is needed.

The amount of urease inhibitor (NBPT) needed in given coated ureaformulation often depends upon the soil type and soil pH and the amountof urease activity due to soil bacteria. The quantity of ureaseinhibitor needed in the final granular product treated with the bufferedmixture containing NBPT could be determined by measuring the ureaseactivity in a range of soils and then determining the amount ofinhibitor needed to inhibit that amount of urease in the specific soilwhere the coated products will be applied. The alternative methodinvolves assessing the volatile nitrogen losses from a range of soilsand formulating to achieve a desired amount of control of the volatilenitrogen loss in the specific soil where the coated products will beapplied. The practices for measuring urease inhibition or volatilenitrogen losses are described in the patents or literature referencedabove.

The coating of granular urea with NBPT dissolved in a buffered mixtureof the invention may be accomplished using any commercially availableequipment in which a granular product may be comingled with a liquid.The equipment may permit the buffered mixture liquid containing NBPT tobe sprayed onto the granules as they tumble in the mixer or the bufferedmixture liquid containing NBPT may be dribbled into the granules as theytumble within the mixing equipment. The surface wetted granules fromaddition of the buffered mixture containing NBPT are then tumbled untilthe material has been uniformly distributed across the surface of thegranules. The resulting NBPT treated urea product may then be stored orpackaged as required. A flowability aid or desiccant such as gypsum,silica, monoammonium phosphate, potassium sulfate, potassium magnesiumsulfate or clay may be required to ensure flowability of the resultingcoated granular product if there is inadequate control of the volume ofNBPT containing buffered mixture liquid applied to the coating.Preferably, the buffered mixture liquid containing NBPT is introducedinto the mixing equipment via a metering system able to providereproducible formulations.

The product may be applied to land to provide nitrogen needed by plantsto the soil which contain the valuable urease inhibitor NBPT. Thegranular product materials containing NBPT may be applied using anyroutinely used application method such as broadcast by ground or aerialspreading equipment, banding using ground application equipment andspotting techniques wherein the fertilizer is placed next to the planteither above ground or in a depression made into the soil surface nextto the plant where application is desired.

Another useful set of urea containing formulations may be obtained byadding the buffered mixture containing NBPT to aqueous solutions whichcontain urea. Commercially available UAN solution a mixture of urea andammonium nitrate that may contain from about 28% N to 32% N can be mixedwith the buffered mixture containing NBPT. The mixing of the NBPTcontaining buffered mixture with the UAN solution may be accomplished inany commonly used mixing equipment. Once the NBPT containing bufferedmixture mixture with UAN is prepared, it may be applied to the soil asconventionally practiced for UAN solution without the NBPT containingbuffered mixture.

Another useful set of granular products may be prepared by diluting theNBPT containing buffered mixture with another liquid which may be anaqueous mixture. The resulting diluted NBPT containing mixture can thenbe used to cause powdered plant nutrient supplying materials to adhereto granular urea. Dilution of the NBPT present in the buffered mixturemay be required to avoid using an excessive amount of NBPT in theresulting coated granular products to avoid potential phytotoxicity.

To prepare the diluted NBPT containing mixture the buffered mixturecontaining NBPT can be measured into the diluting material on a weightor volumetric basis. Any order of addition of the ingredients may beused. The maximum amount of NBPT is limited by solubility limit for NBPTin the diluted mixture or aqueous solubility limit of NBPT in thediluted mixture being prepared.

The mixing of the two materials may be accomplished by any commonly usedmethod: for example; simply tank mixing the two materials prior to use,using a metering system to inject both materials simultaneously, ormixing via a spray injection system if the binder was normally sprayedonto a granular bed to prepare coated urea products.

Coated granular urea products containing additional plant nutrients arethen prepared from granular urea, a source or sources of the additionalnutrients in powdered form and the diluted NBPT containing mixturedescribed above. Granular urea is first dampened with the dilutedbuffered NBPT containing mixture followed by mixing to distribute theNBPT containing liquid mixture over the granular urea surface using anycommonly used equipment to comingle a liquid with a granular solid.After distribution of the diluted buffered NBPT containing mixture overthe granular surface, the additional nutrients in powdered form areadded to the dampened mixture and the resulting combined ingredients arefurther mixed to distribute the powdered materials. In an alternateapproach the powdered materials may be first mixed with the granularurea and then the buffered NBPT containing diluted mixture is sprayedonto a tumbling bed of the dry ingredients to agglomerate the drymaterials. This later method is particularly suited to continuousprocessing.

As an embodiment of the invention, a buffered mixture is prepared fromMEA and acetic acid with a pH from 8.5-9.5 and then, NBPT is dissolvedby melting the compound with sufficient buffered mixture to give about15% by weight of NBPT. The resulting buffered NBPT containing mixturecan be used to treat urea as described above.

As another embodiment of the invention, a buffered mixture is preparedfrom TEA and acetic acid with a pH of 8.5-9.5 and then NBPT is dissolvedby melting the compound with sufficient buffered mixture to give aconcentration of 30% NBPT. The resulting buffered NBPT containingmixture can be used to treat urea as described above.

As another embodiment of the invention, a buffered mixture is preparedfrom MIPA and acetic acid with a pH of 8.5-9.5 and then NBPT isdissolved by melting the compound with sufficient buffered mixture togive a concentration of 25% NBPT. The resulting buffered NBPT containingcan be used to treat urea as described above.

As another embodiment of the invention, a buffered mixture is preparedfrom DIPA and acetic acid with a pH of about 9 and then NBPT isdissolved by melting the compound with sufficient buffered mixture togive a concentration of NBPT up to the solubility limit. The resultingbuffered NBPT containing mixture can be used to treat urea as describedabove.

As another embodiment of the invention, any of the NBPT containingbuffered mixtures prepared according to the invention may be diluted byadding a co-diluent such as ethylene glycol or propylene glycol toreduce the viscosity of the buffered NBPT containing mixture.

In another embodiment of the invention, commercially available mixturesof MEA, DEA and TEA may be used to prepare a buffered mixture byreaction of the mixture of amino alcohols with acetic acid to reach a pHof about 9. The resulting buffered mixture is used to dissolve NBPT upto the solubility limit by melting the compound into the bufferedmixture. The NBPT containing buffered mixture may be used to treat ureaas described above.

In another embodiment of the invention, a buffered solution prepared asdescribed above containing up to about 3.0% by weight NBPT can bedissolved in the triethanolamine borate mixture such as ARBORITE® Binder78. The resulting mixture could then be used to prepare coated ureagranules with both NBPT and a boron compound present as described above.

As another embodiment of the invention, a mixture containing up to about2% NBPT can be prepared by first making a buffered mixture oftriethanolamine and acetic acid as indicated above and then dissolvingup to about 20% NBPT in the buffered mixture as described above thenmixing the solution (buffered solution containing NBPT) with UANsolution to give a final concentration of NBPT of about 3%. Preferablythe concentration of NBPT in the UAN solution would range from about0.05% to about 0.25% by weight. The liquid formulation may then useddirectly as a fertilizer solution.

In another embodiment of the invention, a solution containing up toabout 15% NBPT dissolved in a buffered mixture of triethanolamine andacetic acid with a pH from 8.5 to 9.5 may be diluted with ARBORITE®Binder 75 to prepare a solution which contains both boron and NBPT. Theresulting diluted NBPT solution may then be used to prepare coated ureagranules with NBPT, boron and optionally other plant nutrients asindicated above.

When the diluent liquid contains an aqueous ethanolamine borate such asARBORITE® Binder 75, a secondary or tertiary amino alcohol may be neededto stabilize the mixture. The secondary or tertiary amino alcoholconcentration should be kept above about 12% and preferably above about20% in the final diluted mixture. Below a 12% concentration of thesecondary or tertiary amino alcohol in an ethanolamine borate solution asuspension of NBPT in the aqueous mixture may form which requiresconstant agitation to be used to prepare other products.

EXAMPLES

The following examples are provided to illustrate the practice of theinvention. The examples are not intended to illustrate the completerange of compositions possible.

The following abbreviations are employed: MEA (ethanolamine), TEA(triethanolamine), MIPA (monoisopropanolamine or 1-amino-2-propanol) andNBPT (N-n-butylthiophosphoric triamide) UAN (urea ammonium nitratesolution). The term powdered when used is understood to refer to anyfinely divided material with a particle size less than 250 μm (60 mesh).

In many of the following examples the term melted is used to describethe process of dissolving NBPT into a buffered solvent system. The termmelted within this context refers to the heating of the mixture of NBPTand the coating solvent to dissolve the NBPT into the coating solvent.The dissolution step requires a temperature of between 50° C. and 60° C.

Many of the examples which follow require the reaction of a compoundwith basic nitrogen containing group and a carboxylic acid. The productsof this type of reaction are the ammonium ion of the compound containingthe nitrogen atom and the carboxylate anion of the carboxylic acidemployed and water. One mole of each reaction product will form when 1mole of the basic nitrogen containing group is reacted with 1 mole of anacid.

When an excess of the compound containing the nitrogen atom is presentthe mixture will have an excess of this nitrogen containing compoundremaining. That excess is referred to as an un-reacted nitrogencontaining compound. Inherent ionization reactions of the basic nitrogencontaining group are not included when calculating the molarcompositions of the reaction products.

Example 1

A buffered mixture was prepared by reacting 201.0 grams of a 85% aqueousMEA solution (2.80 mol MEA, 1.67 mol water) with 182.8 grams of glacialacetic acid (3.04 mol) and allowing the reaction mixture to cool. Thefinal pH of the mixture was 7.0. The final buffered mixture contained0.24 moles of acetic acid (un-reacted) and 2.80 moles of the acetateion, 2.80 moles of the ammonium ion of MEA and 4.47 moles of water.

The buffered mixture was able to dissolve 20% NBPT; however, thematerial turned yellow over time and emitted an odor of hydrogensulfide. The yellowing and hydrogen sulfide odor indicated decompositionof NBPT had occurred.

As another example of the instability of this formulation, the bufferedNBPT containing mixture was added to ARBORITRE® Binder 75 which is anethanolamine borate containing copper (II) ions at about 0.75%. Themixture of the two materials immediately turned brown indicating thepresence of sulfides of copper (II).

Example 2

A coated granular urea product containing NBPT was prepared from thebuffered solvent comprised of MEA and acetic acid of example 1. The twostep process began by melting 10.0 grams of NBPT into 90.0 grams of thefreshly prepared buffered mixture with a pH of 7 of example 1 to achievea solution with 10% NBPT. The second step involved forming the coatedproduct by adding 2.75 g of the buffered solution containing 10% NBPT to500.0 grams of granular urea and the combined ingredients were mixed todistribute the NBPT over the urea granules. The free flowing finalproduct contained 45.77% nitrogen and 0.055% NBPT.

It was discovered that only freshly prepared solutions of NBPT using thebuffered mixture of example I could be used for coating urea as the NBPTcontaining solution caused hydrolysis of the NBPT and released sulfides.

Example 3

A buffered mixture was prepared by reacting 100.0 grams of 85% aqueousMEA (1.64 mol MEA, 0.832 mol water), with 66.6 grams of glacial aceticacid (1.11 mol) and allowing the reaction mixture to cool. The final pHof the mixture was 9.2. The final buffered mixture contained 1.11 mol ofthe ammonium ion of MEA, 1.11 mol of acetate ion, 1.94 mol of water and0.53 mol of un-reacted MEA.

The buffered mixture was able to dissolve 12% NBPT. The buffered mixturecontaining 12% NBPT showed signs of slight crystallization when chilled;however, no signs of yellowing were observed indicating no decompositionof NBPT was occurring.

Example 4

A 10% solution of NBPT in the buffered mixture of example 3 was preparedby melting 20.0 grams of NBPT into 180 g of the buffered mixture ofexample 3 at 50° C.

Example 5

The buffered mixture of example 4 was used to prepare a liquidfertilizer composition by adding 1.40 grams of the buffered mixture ofexample 4 to 40.0 grams of UAN solution (32% N). The final liquidfertilizer contained 0.34% NBPT and 30.9% N.

Example 6

A buffered mixture was prepared by reacting 300.0 grams of TEA (2.01mol) with 44.7 grams of acetic acid (0.744 mol). The final mixture had apH of 7.6. The final mixture contained 0.744 mol of the ammonium ion ofTEA, 0.744 mol of acetate ions, 0.744 mol water and 1.27 mol ofun-reacted TEA.

The buffered mixture was able to hold up to 30% NBPT; however, itdisplayed a tendency to yellow over time indicating decomposition of theNBPT. When a mixture of the buffered mixture containing 20% NBPT wasadded to the copper (II) containing mixture ARBORITE® Binder 75 theresulting admixture lost its characteristic blue color and appearedgreen indicating the presence of sulfides in the buffered mixture at apH of 7.6.

Example 7

A buffered mixture was prepared by reacting 100.0 grams of TEA (0.670mol) with 1.65 grams of acetic acid (0.0275 mol). The final mixture hada pH of 8.5 The final mixture contained 0.0275 mol of the ammonium ionof TEA, 0.0275 mol of acetate ion, 0.0275 mol of water and 0.643 mol ofun-reacted TEA. The buffered mixture was able to dissolve 30% NBPT.

Example 8

A 30% solution of NBPT in the buffered mixture of example 7 was preparedby melting 30.0 g of NBPT into 70.0 of the buffered mixture of example7. The melting step was conducted at 50° C.

Example 9

A coated granular urea product was prepared from the 30% NBPT containingsolution of example 8 by mixing 1.0 grams of the 30% containing NBPTsolution of example 8 with 500.0 grams of urea and mixing the combinedingredients to distribute the NBPT over the urea surface. The final freeflowing product contained 45.90% nitrogen and 0.060% NBPT.

Example 10

The buffered mixture of example 8 was diluted by mixing 1.25 g of the30% NBPT containing solution (example 8) with 12.63 grams of a thebuffered mixture of example 7 to reduce the NBPT concentration to 2.7%.The diluted mixture containing 2.7% NBPT was used to prepare thephosphate coated urea of example 11.

Example 11

A phosphate coated urea was prepared by adding 13.88 grams of thediluted buffered mixture of example 10 (2.7% NBPT) to 500.0 grams ofurea and mixing in a planetary mixer to distribute the liquid over thegranular urea surface. After distribution of the liquid 107.3 grams ofpowdered monoammonium phosphate (11-52-0) was added and the combinedingredients were mixed to distribute the powder over the granularsurface to obtain a free flowing product. The final product contained39.10% nitrogen, 8.98% P2O5 and contained 0.060% NBPT.

Example 12

A buffered mixture was prepared by reacting 100.0 grams of MIPA (1.33mol) with 59.7 grams of acetic acid (0.994 mol). The final colorlessmixture had a pH of 9.0. The final buffered mixture contained 0.994 molof the ammonium ion of MFPA, 0.994 mol of acetate ions, 0.994 mol waterand 0.337 mol of un-reacted MIPA. The buffered mixture was able todissolve about 30% NBPT.

Example 13

A 25% NBPT containing solution was prepared from the buffered mixture ofexample 12 by melting 15.8 grams of NBPT into 47.5 grams of the bufferedmixture of example 12. The NBPT containing buffered mixture was thenadded to ARBORITE® Binder 75. No reaction characteristic of theformation of sulfide salts of copper (II) was observed.

Example 14

The 25% NBPT containing buffered mixture of example 13 was used toprepare a coated urea fertilizer composition. 1 drop of a 1% aqueousmixture of methylene blue was added to 2.00 grams of the mixture ofexample 13 and then that mixture was added to 500.0 grams of granularurea. The combined ingredients were mixed in a planetary mixture todistribute the liquid over the surface of the granular urea. Afree-flowing granular product was obtained with a faint blue color. Thegranular coated urea product contained 0.10% NBPT, with a nitrogencontent of 45.81%.

Example 15

A buffered mixture solution containing 20% NBPT was prepared from thebuffered mixture of example 7 comprised of triethanolamine and aceticacid at a pH of 8.5. 20.0 grams of NBPT was melted into 80.0 grams ofthe buffered mixture of example 7 at 50° C.

Example 16

A liquid fertilizer solution was prepared from the 20% NBPT containingbuffered mixture of example 15 by adding 1.50 grams of the bufferedmixture of example 15 to 40.0 grams of liquid UAN solution (32% N). Thefinal liquid fertilizer mixture contained 0.72% NBPT and 30.8% N.

Certain modifications and improvements will occur to those skilled inthe art upon a reading of the foregoing description. It should beunderstood that all such modifications and improvements have beendeleted herein for the sake of conciseness and readability but areproperly within the scope of the following claims.

1. A method of preparing a solution for use in reducing the volatilityof urea fertilizers comprising dissolving N-(n-butyl)-thiophosphorictriamide (NBPT) in a mixture of an amino alcohol having the formula1—(H)_(x)—N—((CH₂)_(m)—OH)_(n) where m is 1-3, x is 0 or 1, and n is 2when x is 1 and 3 when x is 0: or the formula2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of the carbonchain where the secondary hydroxyl group is located is 3, y is 0 or 1,and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acid having 6or fewer carbon atoms to form an NBPT solution.
 2. The method of claim1, wherein said amino alcohol is selected from the group consisting ofdiethanolamine, dipropanolamine, triethanolamine, tripropanolamine,diisopropanolamine, triisopropanolamine, and mixtures thereof.
 3. Themethod of claim 1, wherein from about 15% to about 30% by weight NBPT isdissolved in said mixture.
 4. The method of claim 1, wherein said NBPTis dissolved in said mixture and a co-solvent selected from the groupconsisting of ethylene glycol and propylene glycol.
 5. The method ofclaim 1, wherein said amino alcohol has a pK_(a) of between about 7.5and 10 and said acid has a pK_(a) of 5 or less.
 6. A solution for use inreducing the volatility of urea fertilizers comprisingN-(n-butyl)-thiophosphoric triamide (NBPT) dissolved in a mixture of anamino alcohol having the formula 1—(H)_(x)—N—((CH₂)_(m)—OH)_(n) where mis 1-3, x is 0 or 1, and n is 2 when x is 1 and 3 when x is 0: or theformula 2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of thecarbon chain where the secondary hydroxyl group is located is 3, y is 0or 1, and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acidhaving 6 or fewer carbon atoms to form an NBPT solution.
 7. The solutionof claim 6, wherein said amino alcohol is selected from the groupconsisting of diethanolamine, dipropanolamine, triethanolamine,tripropanolamine, diisopropanolamine, triisopropanolamine, and mixturesthereof.
 8. The solution of claim 6, wherein from about 15% to about 30%by weight NBPT is dissolved in said mixture.
 9. The solution of claim 6,further including a co-solvent.
 10. The solution of claim 6, whereinsaid solution is diluted with water.
 11. A method of producing reducedvolatility of urea fertilizers comprising: a) dissolvingN-(n-butyl)-thiophosphoric triamide (NBPT) in a mixture of an aminoalcohol having the formula 1—(H)_(x)—N—((CH₂)_(m)—OH)_(n) where m is1-3, x is 0 or 1, and n is 2 when x is 1 and 3 when x is 0: or theformula 2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of thecarbon chain where the secondary hydroxyl group is located is 3, y is 0or 1, and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acidhaving 6 or fewer carbon atoms to form an NBPT solution; and b)combining said NBPT solution with said urea fertilizer.
 12. The methodof claim 11, wherein said urea fertilizer is in the form of granules andsaid NBPT solution is coated on said granules.
 13. The method of claim11, wherein said fertilizer granules are coated with from about 0.050%to about 0.25% NBPT.
 14. The method of claim 11, wherein said ureafertilizer is an aqueous urea fertilizer solution and said NBPT solutionis mixed with said aqueous solution.
 15. The method of claim 11, whereinsaid aqueous urea fertilizer solution contains with from about 0.050% toabout 0.25% NBPT
 16. The method of claim 11, wherein said amino alcoholis selected from the group consisting of diethanolamine,dipropanolamine, triethanolamine, tripropanolamine, diisopropanolamine,triisopropanolamine, and mixtures thereof.
 17. The method of claim 11,wherein from about 15% to about 30% by weight NBPT is dissolved in saidmixture of an amino alcohol and a carboxylic acid.
 18. A method ofproducing reduced volatility of urea fertilizers comprising: a)dissolving N-(n-butyl)-thiophosphoric triamide (NBPT) in a mixture of anamino alcohol having the formula 1—(H)_(x)—N—((CH₂)_(m)—OH)_(n) where mis 1-3, x is 0 or 1, and n is 2 when x is 1 and 3 when x is 0: or theformula 2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of thecarbon chain where the secondary hydroxyl group is located is 3, y is 0or 1, and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acidhaving 6 or fewer carbon atoms to form an NBPT solution; and b)combining a granular urea fertilizer with said NBPT solution.
 19. Themethod of claim 18, further including the step of coating saidfertilizer granules with powdered micronutrients.
 20. The method ofclaim 18, wherein said NBPT solution is diluted with an aqueous mixtureprior to addition of micronutrients.
 21. The method of claim 18, whereinsaid granular urea fertilizer with added micronutrients contains fromabout 0.050% to about 0.25% NBPT.
 22. A method of producing reducedvolatility liquid urea fertilizer comprising: a) dissolvingN-(n-butyl)-thiophosphoric triamide (NBPT) in a mixture of an aminoalcohol having the formula 1—H)_(x)—N—((CH₂)_(m)—OH)_(n) where m is 1-3,x is 0 or 1, and n is 2 when x is 1 and 3 when x is 0: or the formula2—(H)_(y)—N—((CH₂)—CHOH—CH₃)_(z) such that the length of the carbonchain where the secondary hydroxyl group is located is 3, y is 0 or 1,and z is 2 when y is 1 and 3 when y is 0, and a carboxylic acid having 6or fewer carbon atoms to form an NBPT solution; and b) mixing said NBPTsolution with an aqueous solution of urea fertilizer.
 23. The method ofclaim 22, wherein said amino alcohol is selected from the groupconsisting of diethanolamine, dipropanolamine, triethanolamine,tripropanolamine, diisopropanolamine, triisopropanolamine, and mixturesthereof.
 24. The method of claim 22, wherein from about 15% to about 30%by weight NBPT is dissolved in said mixture.
 25. The method of claim 22,wherein sufficient NBPT solution is mixed with said aqueous solution toproduce an aqueous fertilizer containing from about 0.050% to about0.25% NBPT.
 26. The method of claim 22, wherein said urea fertilizer isan aqueous mixture of urea and ammonium nitrate.